The present invention relates to an angular velocity sensor used in a vehicle brake control or a roll air bag system.
A conventional angular velocity sensor is disclosed, for example, in Electrical Equipment Technical Conference Report (Vol. 38, No, 3, 1994, pp. 26-33). The angular velocity sensor comprises an exciter for providing a tuning fork vibrator with vibration, a detector for detecting the vibration level of the vibrator, a detector for detecting a Coriolis force generated depending on an angular velocity, a first amplifier for amplifying the output of the detector for detecting the vibration level, and a variable gain amplifier connected to the exciter for maintaining a constant amplitude of the tuning fork vibrator by varying the gain according to the output of a comparator. The variable gain amplifier amplifies a voltage shifted in phase by 90 degrees from the output voltage of the first amplifier.
The conventional sensor hardly detects a breakage of a connection line between a detecting electrode and a detecting circuit, a sensitivity change due to a deterioration of the detection electrode, or trouble in the detection circuit, and accordingly, hardly has reliability.
The invention is intended to solve the problems of the prior art, and it is hence an object thereof to present an angular velocity sensor for detecting a trouble or a deterioration of itself.
To solve the problems, the invention presents an angular velocity sensor comprising an element section including a first exciter for providing a vibrator with drive vibration, a vibration detector for detecting the vibration level of the vibrator, and a piezoelectric element having at least two Coriolis detectors for detecting Coriolis vibration generated depending on an input angular velocity, and also comprising a circuit section including a driving circuit receiving a signal from the vibration detector and issuing a signal to the first exciter and a detection circuit for receiving signals from the Coriolis detectors. The circuit section further comprises a level judging circuit for judging an abnormal level of electric charges occurring in the Coriolis detectors and output means for issuing an output when detecting an abnormality. Each output of Coriolis detectors contains independently a drive vibration component larger than the reference level of the level judging circuit. And the layout of the electrodes the element section is adjusted so that the combined output may contains the vibration component smaller than the reference level. And therefore, if one of input lines from the Coriolis detector to the detection circuit is broken, this abnormality can be detected by the level judging circuit.